The
core X protocol allows only applications to explicitly sound the system
bell with a given duration, pitch, and volume. Xkb extends this capability
by allowing clients to attach symbolic names to bells, disable audible
bells, and receive an event whenever the keyboard bell is rung. For the
purposes of this document, the audible bell is defined to be the system
bell, or the default keyboard bell, as opposed to any other audible sound
generated elsewhere in the system. You can ask to receive XkbBellNotify
events when any client rings any one of the following:

The default bell

Any bell on an input device that can be specified by a bell_class and bell_id
pair

Any bell specified only by an arbitrary name. (This is, from the server's
point of view, merely a name, and not connected with any physical sound-generating
device. Some client application must generate the sound, or visual feedback,
if any, that is associated with the name.)

You can also ask to receive
XkbBellNotify events when the server rings the default bell or if any
client has requested events only (without the bell sounding) for any of
the bell types previously listed.

You can disable audible bells on a
global basis. For example, a client that replaces the keyboard bell with
some other audible cue might want to turn off the AudibleBell control
to prevent the server from also generating a sound and avoid cacophony.
If you disable audible bells and request to receive XkbBellNotify events,
you can generate feedback different from the default bell.

You can, however,
override the AudibleBell control by calling one of the functions that
force the ringing of a bell in spite of the setting of the AudibleBell
control - XkbForceDeviceBell or XkbForceBell. In this case the server
does not generate a bell event.

Just as some keyboards can produce keyclicks
to indicate when a key is pressed or repeating, Xkb can provide feedback
for the controls by using special beep codes. The AccessXFeedback control
is used to configure the specific types of operations that generate feedback.

Bell Names

You can associate a name to an act of ringing a bell by converting
the name to an Atom and then using this name when you call the functions
listed in this chapter. If an event is generated as a result, the name
is then passed to all other clients interested in receiving XkbBellNotify
events. Note that these are arbitrary names and that there is no binding
to any sounds. Any sounds or other effects (such as visual bells on the
screen) must be generated by a client application upon receipt of the
bell event containing the name. There is no default name for the default
keyboard bell. The server does generate some predefined bells for the AccessX
controls. These named bells are shown in Table 1; the name is included
in any bell event sent to clients that have requested to receive XkbBellNotify
events.

Table 1 Predefined Bells

Action Named Bell

Indicator turned on AX_IndicatorOn

Indicator
turned off AX_IndicatorOff

More than one indicator changed state AX_IndicatorChange

Control
turned on AX_FeatureOn

Control turned off AX_FeatureOff

More than one control
changed state AX_FeatureChange

SlowKeys and BounceKeys about to be turned
on or off

AX_SlowKeysWarning

SlowKeys key pressed AX_SlowKeyPress

SlowKeys
key accepted AX_SlowKeyAccept

SlowKeys key rejected AX_SlowKeyReject

Accepted
SlowKeys key released AX_SlowKeyRelease

BounceKeys key rejected AX_BounceKeyReject

StickyKeys
key latched AX_StickyLatch

StickyKeys key locked AX_StickyLock

StickyKeys key
unlocked AX_StickyUnlock

Audible Bells

Using Xkb you can generate bell
events that do not necessarily ring the system bell. This is useful if
you need to use an audio server instead of the system beep. For example,
when an audio client starts, it could disable the audible bell (the system
bell) and then listen for XkbBellNotify events. When it receives a XkbBellNotify
event, the audio client could then send a request to an audio server to
play a sound.

You can control the audible bells feature by passing the
XkbAudibleBellMask to XkbChangeEnabledControls. If you set XkbAudibleBellMask
on, the server rings the system bell when a bell event occurs. This is
the default. If you set XkbAudibleBellMask off and a bell event occurs,
the server does not ring the system bell unless you call XkbForceDeviceBell
or XkbForceBell.

Audible bells are also part of the per-client auto-reset
controls.

Bell Functions

Use the functions described in this section to
ring bells and to generate bell events.

The input extension has two types
of feedbacks that can generate bells - bell feedback and keyboard feedback.
Some of the functions in this section have bell_class and bell_id parameters;
set them as follows: Set bell_class to BellFeedbackClass or KbdFeedbackClass.
A device can have more than one feedback of each type; set bell_id to
the particular bell feedback of bell_class type.

Table 2 shows the conditions
that cause a bell to sound or an XkbBellNotifyEvent to be generated when
a bell function is called.

Table 2 Bell Sounding and Bell Event Generating

Function called AudibleBell Server sounds a bell Server sends an

XkbBellNotifyEvent

XkbDeviceBell On Yes Yes

XkbDeviceBell Off No Yes

XkbBell On Yes Yes

XkbBell Off No Yes

XkbDeviceBellEvent On
or Off No Yes

XkbBellEvent On or Off No Yes

XkbDeviceForceBell On or Off Yes No

XkbForceBell On
or Off Yes No

If a compatible keyboard extension isn't present in the X server,
XkbForceDeviceBell immediately returns False. Otherwise, XkbForceDeviceBell
rings the bell as specified for the display and keyboard device and returns
True. Set percent to be the volume relative to the base volume for the
keyboard as described for XBell.

There is no name parameter because
XkbForceDeviceBell does not cause an XkbBellNotify event.

You can call
XkbBell without first initializing the keyboard extension.

Xkb
generates XkbBellNotify events for all bells except for those resulting
from calls to XkbForceDeviceBell and XkbForceBell. To receive XkbBellNotify
events under all possible conditions, pass XkbBellNotifyMask in both
the bits_to_change and values_for_bits parameters to XkbSelectEvents.

The XkbBellNotify event has no event details. It is either selected or
it is not. However, you can call XkbSelectEventDetails using XkbBellNotify
as the event_type and specifying XkbAllBellNotifyMask in bits_to_change
and values_for_bits. This has the same effect as a call to XkbSelectEvents.